Free piston engine ignition apparatus

ABSTRACT

Apparatus and method features are disclosed for initiating combustion in free piston engines in response to a movementrelated characteristic of the power piston, such as its rate of change of position in the power cylinder of the engine, so that combustion is caused to occur at a desired time which is related to the time the power piston reverses direction at the start of a power stroke, without regard to variations from one stroke to another in the actual physical position of the power piston along its path of movement in the power cylinder at the moment of piston reversal. Various means are shown or suggested for sensing piston movement and causing combustion in response to changes in the velocity or acceleration of such piston movement at a controlled time interval before or after such velocity drops to zero or after such velocity has reached a maximum, i.e., at or near the moment when the piston reaches its inner dead point in the power cylinder, and preferably somewhat before that moment. Specific means disclosed for this purpose include means for sensing a desired movement-related characteristic near the end of the stroke and developing a signal dependent, for example, upon the rate of such movement or upon the acceleration of the piston. In one form, an auxiliary piston is moved in synchronism with the movement of the power piston to create, in an auxiliary compression chamber, a pressure signal related to the velocity of the power piston. The pressure signal thus created is then referred to suitable control means where the sensing signal is utilized, for example, by comparison with a reference means, to provide a control force or signal, which is employed to operate a combustion-causing means, such as a spark plug ignition circuit. The reference force for use with such a pressure signal may be obtained by the use of an adjustable spring-biased second auxiliary piston and a controlled orifice. More specifically, the pressure signal created by the first auxiliary piston and cylinder is modified or affected by the rate of flow through the controlled orifice, and the resultant pressure acts on the second auxiliary piston to actuate conventional ignition breaker points against the action of the adjustable spring. The points, in turn, control the delivery of electrical energy to the spark plug. In one embodiment shown, the pressure created by the first auxiliary piston is also used to control the rate of flow through the controlled orifice and thus further determine the point in time at which ignition will be initiated to maintain the proper timing of ignition in spite of variations in the cycle-to-cycle value of power piston velocity or stroke.

United States Patent Feb. 22,

Braun [54] FREE PISTON ENGINE IGNITION APPARATUS [72] Inventor: Anton Braun, 6421 Warren Avenue, Minneapolis, Minn. 55435 [22] Filed: Aug. 24, 1970 [21] Appl. No.: 66,385

521 user. .....123/46R, 60/14, 60/17, 60/DIG. 1, 123/179 BG [51] Int. Cl ..F02b 71/00, F02n 17/00 [58] Field of Search ..l23/46'R, 46 A, 46 B, 46 SC, 123/179 BG; 60/14, 14 B, 17, DIG. 1

[56] References Cited UNITED STATES PATENTS 929,696 8/1909 Oberly 123/46 R X 1,732,694 10/1929 Pescara ..123/46 R 2,423,720 7/1947 Mullesans et al.. .....l23/46 R 2,434,877 1/1948 Welsh et al ..123/46 R 2,462,745 2/1949 Horgen ..l23/46 R 2,983,098 5/1961 Bush ..123/46 R 2,918,788 12/1959 Wochsmuth ...........60/l4 B 5.0! 1,120 1/1963 McCrory et ul. ...............123/46 R Primary Examiner-Wendell E. Burns Attorney-Frederick E. Lange, William C. Babcock and Eugene L. Johnson [57] ABSTRACT a 19.the.11mg mr vsnrisi -rrysr rec at PISTON MOVEMENT J1 SENSING MEANS i MEANS I l NCE l l LL E E E Jo CONTROL MEANS i nmms MEANS s tart-of a power stroke without r d Maria tionsjromone stroke to another in the actual physical position of the power piston along its path of movement in the power cylinder at the moment of piston reversal. Various means are shown or suggested for sensing piston movement and causing combustion in response to changes in the velocity or acceleration of such piston movement at a controlled time interval before or after such velocity drops to zero or after such velocity has reached a maximum, i.e., at or near the moment when the piston reaches its inner dead point in the power cylinder, and preferably somewhat before that moment.

Specific means disclosed for this purpose include means for sensing a desired movement-related characteristic near the end of the stroke and developing a signal dependent, for example, upon the rate of such movement or upon the acceleration of the piston. In one form, an auxiliary piston is moved in synchronism with the movement of the power piston to create, in an auxiliary compression chamber, a pressure signal related to the velocity of the power piston. The pressure signal thus created is then referred to suitable control means where the sensing signal is utilized, for example, by comparison with a reference means, to provide a control force or signal, which is employed to operate a combustion-causing means, such as a spark plug ignition circuit. The reference force for use with 'such a pressure signal may be obtained by the use of an adjustable spring-biased second auxiliary piston and a controlled orifice. More specifically, the pressure signal created by the first suxlllary piston and cylinder is modified or ttffcclcd hy the rate of flow through the controlled orifice, and the resultant pressure acts on the second auxiliary piston to actuate conventional ignition breaker points against the action of the adjustable spring. The points, in turn, control the delivery 10f electrical energy to the spark plug. In one embodiment i shown, the pressure created by the first auxiliary piston is also used to control the rate of flow through the controlled orifice and thus further determine the point in time at which ignition will be initiated to maintain the pro r timing of ignition in lspite of variations in the cycle-to-cyc e value of power piston velocity or stroke.

17 Claims, 8 Drawing Figures FREE PISTON 0 ENGINE COMBUSTION CAUSING MEANS FREE PISTON ENGINE IGNITIoN APPARATUS BACKGROUND Combustion is initiated by many techniques in prior art free piston engines. The most common technique uses a direct mechanical link to a piston, and combustion is initiated by means of this mechanical link at a specific linear position of the piston. Examples of this technique include combustion initiating apparatus directly geared to the piston movement, or the use ofa cam surface on the reciprocating piston and a cam follower riding on the cam surface to actuate the combustion initiating apparatus. Other previously used combustion initiating techniques include those where the piston movement controls the firing gap of the spark device directly, and combustion is initiated when the piston approaches sufficiently close to a fixed projection within the power cylinder; those where the linear position of the power piston is magnetically sensed as it approaches a fixed position in the cylinder, and combustion is initiated at that same position in each stroke; and those where a fixed minimum volume of the power cylinder is sensed by using it as a resonant chamber, and combustion is initiated when this minimum volume is achieved.

-All of these methods have a significant drawback in connection with a free piston engine in that combustion is initiated only when the power piston reaches a fixed point in its path of movement within the power cylinder. If the piston does not reach this fixed point, there is no ignition. The piston may not reach this fixed point in the power cylinder for various reasons, including an earlier misfire. Thus, ifa misfire occurs, and there is not sufficient power developed in the engine to provide the energy necessary to return the power piston all the way back to the position necessary to again initiate combustion, the engine will tend to stop, since combustion will not thereafter occur.

In conventional internal combustion engines, these methods do not have a serious drawback, since there is usually a crankshaft and often a flywheel havingconsiderable mass. The result is that ifduring one cycle-the firing occurs prematurely or fails, the mass of the motion transmitting mechanism is such as to carry the conventional engine through a full stroke to another cycle. In free piston engines, however, the piston does not have any crankshaft and flywheel means requiring it to move the same distance in each stroke. Thus, in a free piston engine which provides successive power strokes for the power piston in only one direction, if a misfire occurs, there may be insufficient return energy to return the piston far enough to reach the same predetermined linear position in the power cylinder which would be necessary to again initiate combustion. Thus, the engine will actually stop.

SUMMARY The apparatus according to the invention solves this and other problems of the prior free piston engine art by initiating combustion around the point in the cycle where the power piston within the engine reverses direction, without regard to variations in the physical or linear position of the power piston within the power cylinder at the moment the piston reverses direction at the start of successive power strokes. Thus, combustion is initiated, according to this invention, at a substantially preselected time close to the time the power piston stops in its cylinder and reverses direction, even though the actual physical position of the power piston in its cylinder at this point in time may vary considerably from one stroke to another.

The apparatus and method of this invention have the advantage that, in the event ofa misfire, the engine will only lose power temporarily and then regain full power. More specifically, the engine will regain full power in a few strokes, even if there is insufficient energy, immediately after the misfire, to fully return the power piston to its desired normal operating inner dead point or top dead center position in the power cylinder, since combustion is started at some point for each power stroke of the power piston. Thus, just before, when, or

' after the power piston stops and begins to reverse direction,

whatever its position in the power cylinder may be, combustion will be initiated. This combustion, although less effcient as compared to combustion at the normal ignition point for a full piston stroke, will supply sufficient energy to the power piston to return it to a point closer to a desired inner dead point than achieved during the return stroke immediately following the misfire. After a number of these less efficient power strokes, the desired inner dead point of the power piston will again be reached. Thus, in contrast to the prior art, a misfire will not cause the engine to stop and necessitate restarting. Under certain conditions, the transitional power strokes may even be more efficient, but the present invention can gradually bring the successive strokes to the desired inner reversal point.

Briefly, the present invention provides an improved method for controlling combustion in a free piston engine which has a power cylinder, and a freely reciprocating power piston moving within the power cylinder. In a preferred method, combustion is initiated at a substantially preselected time before the moment when the power piston reverses direction in the power cylinder at the start of each power stroke, without regard to variations in the actual reversal position of the power piston within the cylinder from one stroke to another. The method comprises the steps of sensing a movement related parameter of the power piston or any other mass within the engine which is connected to or moving in a fixed relation with the power piston, providing an output or sensing signal analogous to the movement related parameter sensed; measuring the sensing signal output, for example, by comparing it to a predetermined reference (which may even be the sensing signal itself) and causing or initiating combustion in the power cylinder in response to a predetermined signal, for example, when the sensed output and the reference achieve a preselected relationship.

A preferred embodiment of apparatus according to the present invention briefly includes sensing means which is responsive to a movement-related power piston characteristic or parameter which has a predeterminable relationship to the moment when the power piston reaches a reversal point at the end of each compression stroke and which is substantially independent of variations in the actual linear position of the power piston within the cylinder at the moment of piston reversal for different power strokes. This sensing means provides a sensing signal analogous to the instantaneous values of the movement-related power piston characteristic. The sensing signal is fed to a control means which in turn actuates the combustion-causing means at the desired moment in time related to the piston reversal. The control means includes adjustable timing or time-delay means to vary the desired time relationship between the actuation of the combustion-causing means and the moment of piston reversal at the end of the compression stroke.

In one preferred embodiment, the sensing apparatus takes the form ofa first auxiliary piston which is reciprocally movable along the longitudinal central axis of an auxiliary pressure cylinder to vary the pressure ofa fluid within the auxiliary cylinder in relation to the velocity of the power piston. The pressure created by the first auxiliary sensor or compressor piston within the auxiliary pressure cylinder in relation to the velocity of the power piston. The pressure created by the first auxiliary sensor or compressor piston within the auxiliary pressure cylinder serves as a sensing signal which is applied to suitable control means, for example, a measuring apparatus which compares this pressure signal to a suitable reference means. The control means then provides a properly timed output signal to the combustion-causing means or controlled power source to initiate combustion at the desired time for each power stroke.

Other types of sensing and control apparatus may also be used. For example, the sensing apparatus may be one which uses other fluidic means, either gaseous or liquid, or various electrical means, such' as an electric generator or an electromagnetic transducer, to provide a sensing signal in any of a number of different forms. The control apparatus or means may also include electric circuitry equivalent to or in combination with the pressure generating and comparing sensors and control devices specifically shown and described herein.

Accordingly, it is a primary object of the present invention to provide a method and apparatus for controlling combustion within a free. piston engine in a manner related in time to the moment of reversal of direction of the power piston within its power cylinder at the end of each compression stroke, without regard to variations in the actual physical position of the power piston within the power cylinder at the moment of such reversal, from one such stroke to another.

This and further objects and advantages of the present invention will become clearer in the light of the following detailed description of an illustrative embodiment of the invention described in connection with the drawings.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of apparatus embodying the present invention;

FIG. 2 is a combined schematic and diagrammatic view ofa free piston engine showing details of one embodiment in which combustion is initiated according to the present invention in response to pressure signals generated in response to a movement-related power piston characteristic;

FIG. 3 is a partial view of a modified form of the apparatus shown in FIG. 2; I

FIG. 4 is a partial sectional view on the line 4--4 of FIG. 3;

FIG. 5 is a view similar to FIG. 2 of another modification;

FIG. 6 is a partial sectional view on the line 6-6 of FIG. 5;

FIG. 7 is an enlarged view, partly in section, of an accelera tion-responsive portion of the control means of the embodiment of FIG. 5; and

FIG. 8 is a partial schematic and sectional view of another embodiment of the invention.

Where used in the various figures of the drawings, the same numerals designate the same or similar parts. Furthermore, when the terms right, left, right end." and left end" are used herein, it should be understood that these terms have reference only to the structure shown in the drawings as it would appear to a person viewing the drawings and are utilized only to facilitate describing the invention.

DESCRIPTION In FIG. 1, a combination of elements according to the present invention is shown schematically in block diagram.

form. Block 10 represents a free piston engine which includes a power piston freely reciprocating within a power cylinder as described below. Block 11 represents sensing means responsive to a movement-related power piston characteristic. Such a characteristic is sometimes referred to herein as a parameter. This movement-related parameter sensing means may sense the velocity or acceleration of a free piston itself, or of some other moving mass which is connected in such a manner that it moves in a fixed relation, i.e., synchronously, with the power piston within the engine. The sensing means provides a suitable sensing signal, such as a pressure created by such a piston or mass within the engine, afiuidflow produced by such a piston or mass within the engine, a voltage output of a generator run by such a free piston or mass within the engine, or some other signal which is a measure of the selected parameter and is thus related to the movement of such a free piston or mass within the engine.

For the purposes of the present invention, a movement-related power piston characteristic or parameter is defined broadly to be any characteristic which has a predeterminable relationship to the moment when the power piston reaches a reversal point at the end of each compression stroke, and which is substantially independent of variations in the actual physical position of the piston within its cylinder at the moment of piston reversal for different power strokes. Thus one such parameter sensing means gives a signal which is an indication of the movement or rate of change of the position of the power piston within the free piston engine, as distinguished from the position of the piston or other mass. For the purposes of the present invention, a movement-related parameter is to be contrasted with a displacement parameter which directly indicates the position or displacement of the power piston. Examples of such displacement parameters are displacements or positions of parts mechanically linked to the moving power piston within a free piston engine and the displacement or position of a cam follower riding on a cam surface fixed to the power piston within thefree piston engine.

Sensing means 11 provides an indication or sensing signal analogous to the sensed parameter and such signal is fed to suitable control means represented by block 12.. Control means 12 utilizesor processes the sensing signal to achieve the desired ignition timing. For example, this control means includes a block 13 representing suitable measuring ,or reference means. The sensing signal is measured, for example, by comparison to the reference, and the controller then provides whatever impetus or output control function or signal is required to operate the combustion-causing means 16 at the desired time of ignition close to or at the moment of reversal of the power piston at the end of each compression stroke.

The control means 12 preferably includes suitable adjusting or timing means, shown schematically by block 14 to provide the desired timing of the output control signal. Combustion-causing means 16 thus initiates or controls the combustion within the power cylinder of free piston engine 10.

If free piston engine 10 is to operate according to the principles of operation of conventional diesel engines, combustioncausing means 16 may be a fuel injector system, and the output of control means 12 may actuate a fuel pump providing the fuel to the fuel injector system. If free piston engine 10 is to operate in accordance with principles of conventional spark ignition engines, combustion-causing means 16 will include a spark plug, and theoutput of control means 12 may actuate suitable electrical circuit means to provide the necessary voltage to the spark plug. In the case ofa stratified charge engine. both the spark ignition system and the injection system must be controlled accordingly. The spark ignition system has been chosen for convenience in explaining the principles of the present invention.

In FIG. 2, a free piston engine 17 is shown having a power section generally designated 18 located upon the extreme right of the engine and shown in cross section to reveal the schematic representation of a power piston 20 reciprocating along the longitudinal central axis of engine 10 within a power cylinder 21. The housing of engine 17 is generally designated at 22. It is to be understood that the engine is provided with conventional means (not shown) for introducing fuel and exhausting burnt fuel at appropriate times in the engine cycle.

In this case, an inwardly compressing compressor 23 is shown by way of example at the left end of engine 17. A shaft 24 extends horizontally along the longitudinal central axis of engine 17 and interconnects power piston 20 and a compressor piston 26. Compressor piston 26'is arranged to be reciprocally movable along the central longitudinal axis of engine 10 within a compressor cylinder 28. Intake and exhaust valves 30 and 32, respectively, are positioned adjacent the right end of cylinder 28 to provide for the ingress and the egress of fluid to and from a compressor chamber 34 formed between a right face 36 of compressor piston 26 and a left inner face 38 of an inner wall 40.

' power stroke of power piston 20 provides at least part of the energy needed for the return strokes of pistons 20 and 26 to the right.

The engine will also include other known features, the details of which are not essential to an understanding of the present invention. Thus, where shaft 24 penetratesinterior walls 40 and 49, conventional shaft seals (not shown) are provided to prevent the leakage of gas and lubricant around shaft 24 as it reciprocates.

The movement-related power piston parameter sensing means used on engine 17 includes a pressure-signal generator driven by rod 50 which has a base attached to shaft 24 so that rod 50 reciprocates as a unit with shaft 24 and hence with power piston 20. A second shaft 52 has its left end connected to the top portion of rod 50 and its right end connected with a first auxiliary piston 54. Auxiliary piston 54 is arranged to be reciprocally movable within the first auxiliary pressure cylinder 56 to generate pressure signals in the compression chamber 57 within cylinder 56. Cylinder 56 is formed within an auxiliary housing with the cylinder axis parallel to shaft 24 and radially spaced from the central longitudinal axis of engine 17. The left end of cylinder 56 is open to admit shaft 52 and is in communication with an interior chamber 60 formed between interior walls 40 and 49. The right end of cylinder 56, i.e., compressor chamber 57, joins a conduit 62 which serves as sensing output means to transmit the output pressure signal from the sensing means to the control means 12.

Control means 12 is shown in this example as including a second pressure chamber 64 within a second auxiliary cylinder 66. An opening 68 in the sidewall of cylinder 66 is connected to the upper end of conduit 62 and serves as input means for the control system. The pressure signals from sensing means 11 thus are fed from sensing output conduit 62 to the inlet opening or input means 68 of controller 12.

Within chamber 64, the incoming pressure signal is processed to provide an output control impulse or signal to operate the combustion-causing means 16. In this embodiment the incoming pressure signal is processed by comparison with a reference means consisting of a spring loaded second auxiliary piston 70 at the left end 72 ofcylinder 66.

Piston 70 is secured at 74 to the right end of a reciprocally movable output shaft 78. The shaft is supported for sliding movement within an adjustable end cap 80 which is threaded onto the left end 72 of cylinder 66 at 82. Between the end cap 80 and auxiliary piston 70, a spring member 84 is supported to urge the piston 70 and shaft 78 to the right in this figure. 1n effect, spring 84 provides a reference force or signal which tends to urge piston 70 to the right against whatever pressure signals are received and processed within chamber 64 of control means 12. When the pressure in chamber 64 is high enough to overcome the reference force of spring 84, piston 70 and its output shaft 78 will move to the left. When the pressure in chamber 64 drops to a lower point, piston 70 and shaft 78 can then return toward the right to their normal rest position. The left end 72 of cylinder 66 includes a vent opening 86 so that the pressure to the left of piston 70 will at all times correspond to the ambient pressure. Adjustment of end cap 80 to the left or right, by rotating the cap within its threaded connection 82, will change the normal rest position of piston 70, so that a higher or lower pressure in chamber 64 will be required to move the output shaft .78 to the predetermined position at which it will operate the combustion-causing means 16. Thus adjustment of member 80 provides one means for adjusting the timing at which combustion is initiated.

A further adjustment of such timing is provided at the right end 88 of cylinder 66. At this end of the cylinder, pressure chamber 64 is connected through a suitably adjustable orifice or outlet opening, shown substantially at 90, to a discharge conduit 92. Conduit 92 may be open to the ambient pressure, or to some other reference pressure, as desired.

Adjustment of orifice 90 thus provides a further means for controlling the pressure in chamber 64 to achieve the desired timing for movement of output shaft 78.

Movement of shaft 78 at the times determined by pressures within chamber 64 and the spring force on piston 70 provides an output signal or means which is then effectively connected to or fed to the combustion-causing means to cause a properly timed spark in known manner.

More particularly, the left end 94 of shaft 78 contacts a movable portion 116 of breaker points 112 mounted in housing 114 and urges the movable portion 116 against the action of a spring 118 to contact a fixed portion 120 of breaker points 112. Thus, as piston 70 moves horizontally, end 94 of shaft 78 controls the opening or closing of the points 112, i.e., the making or breaking of the contacts formed upon movable portion 116 and stationary portion 120 of breaker points 112.

A wire 122 is connected between movable portion 116 of points 112 and the positive terminal of the battery designated 124. A negative terminal of battery 124 is connected by wire 126 and ground 127 to one grounded terminal 128 of the primary winding 129 of a conventional ignition transformer 130. The other terminal of the primary winding 129 of ignition transformer 130 is connected to fixed portion 120 of breaker points 112 by wire 131. The ungrounded terminal of the secondary winding 132 of transformer 130 is connected to a spark plug 133 by a wire 134 as is usual with such ignition circuits. When the circuit to the primary winding of ignition transformer is first closed by the closing of the points 116 and 120 and is then opened by the separation of the points, a high voltage is produced across the secondary winding, which voltage is applied to the spark plug 133. It will, of course, be understood that any other suitable means may be employed to apply a voltage to plug 133 in response to the actuation of points 116 and 120, or of output shaft 78. Spark plug 133 is shown having its inner end communicating with a combustion chamber 135 formed within cylinder 21 of power section 18.

OPERATION OF THE EMBODIMENT OF FIGS. 1 AND 2 In free piston engine 17, power piston 20 is reciprocally movable within power cylinder 21 between an outer dead point at the left and an inner dead point at the right, i.e., between outer and inner reversal or dead center positions. Unlike a conventional'crank-type engine, these points are not inherently fixed in location. In any case, however, when piston 20 moves to the right so as to compress gases in combustion chamber 135 during a compression stroke, the movement-related parameter sensing means provides a sensed output which has a definite relationship to the time at which movement of power piston 20 stops and the piston reverses direction at the start of its power stroke to the left. If, as in engine 17, the

- desired movement-related parameter to be sensed is velocity,

it will be appreciated by those of ordinary skill in the art that the velocity is a maximum near the center of the rightward compression stroke of the power piston 20 and becomes zero when the power piston reverses direction at each end of the stroke, such that a smooth curve of velocity versus time may be drawn. Combustion can then be initiated during movement of the power piston 20 to the right from its outer dead point to its inner dead point, i.e., at a point in time having a predeterminable time relationship to the moment when the power piston reaches its inner reversal point. During the last part of the compression stroke, the velocity of power piston 20 decreases toward zero. When it reaches a predetermined fixed level below itsmaximum value, the velocity responsive signal can be used to initiate combustion at such a time at or near the moment of piston reversal at the inner dead point as will result in the most desirable combustion, without the necessity of any reference to the actual physical position of the power piston 20 within the power cylinder 21.

The free piston engine 17 of FIG. 2 operates conventionally in that the combustion of gases within combustion chamber applies a force to the right face of power piston 20 and urges it leftward for a power stroke within power cylinder 21. The shaft 24 applies force to compressor piston 26, which also moves leftward to compress the gases within the bounce chamber 42. Also during this time, gas or fluid to be compressed enters compressor chamber 34'Ihr0ugh intake valves 30. When power piston 20 reaches the outer dead point or bottom dead center positiomthe compressed gas or fluid in bounce chamber 42 provides return energy to again move compressor piston 26 to the right to compress the gas within compressor chamber 34, and cause the gas or fluid to pass from compressor chamber 34 through exhaust valve 32. Also, the energy stored within bounce chamber 42 compresses the gases within combustion chamber 134 in preparation for combustion to cause the next power stroke and thus repeat the cycle.

With power piston at its outer dead point, as shown in FIG. 2, sensing piston 54 is at its leftmost position within a cylinder 56. As power piston 20 begins to move rightward on its compressor stroke, piston 54 begins to move rightward and compress fluid within sensing cylinder compression chamber v57. The compressed fluid within compression chamber 57 is fed to control chamber 64, from which it attempts to bleed through control valve 90 and outlet 92. Control valve 90 is adjusted so that the volume rate of air which passes through it in a given unit oftime is less than the volume rate swept by piston 54 in the same unit of time. Thus, the gases within controller compression chamber 64 are compressed. The compression of gases within compression chamber 64 exerts a force upon the second auxiliary piston 70 which is proportional to the gas pressure. Control valve 90 is further adjusted so that the increase in pressure within control chamber 64 exerts a sufficient force upon piston 70 to overcome the reference force supplied to the opposite face of the piston by spring 84. Thus, piston 70 moves to the left. The leftward movement of piston 70 causes a corresponding movement of output shaft 78. End 94 of shaft 78 engages contact 116 and overcomes the retarding force of spring 118 to move contact 116 into electrical engagement with stationary contact 120 to close ignition breaker points 112. Upon the closure of ignition breaker points 112, current begins to flow through the primary of ignition transformer 130 ofFIG. 2.

As power piston 20 and hence auxiliary sensing piston 54 move to the right, power piston 20 first reaches its maximum velocity and then begins to slow as it approaches top dead center or the inner dead point within power cylinder 21. With the slowing of power piston 20, the volume swept by auxiliary sensing piston 54 decreases per unit of time and the pressures created within sensing chamber 57 and control chamber 64 begins to decrease as the gas flows out of control chamber 64 through control valve 90. At a desired preselected time before the inner dead point, depending on the settings of spring retaining knob 80 and control valve 90, the force of spring 84 urging piston 70 to the right overcomes the force exerted upon the right face of piston 70 by the pressure in control chamber 64, and piston 70 again moves to the right to break the electrical contact between ignition breaker points 112. When electrical contact is broken, the secondary winding of ignition transformer 130 has a high-voltage output which is applied through wire 134 to fire spark plug 133 and initiate combustion within combustion chamber 135.

By adjusting the adjustable retaining plug 80, the tension applied to the left face of piston 70 may be controlled, and thus retaining plug 80 gives one adjustment of the timing of the initiation of combustionuFurther, by control of the flow through control valve 90, initiation of combustion may be correctly timed by establishing the time derivative or rate at which the incoming pressure signal will be effective to increase the pressure in control chamber 64.

The apparatus of FIG. 2 thus includes a movement-related power piston parameter sensing means in the form of piston 54, cylinder 56, and compression chamber 57; control means including control pressure chamber 64, with reference means in the form of spring 84, adjustable timing means in the form of retaining knob 80, and control valve 90, and a controlling output means in the form of shaft 78; and combustion-causing means generally including a controlled power source in the form of battery 124, ignition transformer 130, and contacts 116 and 120 of ignition breaker points 112, in combination with combustion initiating means in the form of spark plug 133. The circuitry of FIG. 2 thus operates according to the block diagram of FIG. 1.

In this embodiment, the reference spring and bleed valve are preferably set so that ignition is initiated on the compression stroke of the power piston after the instantaneous piston velocity has passed its maximum value and has decreased to a level which is preselected at between 5 and 30 percent of the normal maximum velocity. Even after a misfire, the pressure in control chamber 64 during the next compression stroke will reach some maximum and then decrease. The control system characteristics are chosen so that such a pressure increase and decrease will initiate combustion on subsequent power strokes, even though the piston does not fully reach its normal inner dead point at the'moment of piston reversal for the power stroke or strokes which follow a misfire.

This operation accordingly offers substantial advantages over prior systems where a particular physical location or position in the power cylinder must be reached by the piston near the end of a compression stroke, before combustion is initiated. In the event of a misfire, combustion will be initiated earlier in the cycle when the apparatus of the present invention is used with the manually adjustable control system described above with respect to FIG. 2. Even with this earlier initiation of combustion, the engine will recover from a misfire, since combustion will still generally be initiated. The apparatus and method of the present invention also allow the incorporation of an automatic change in the control system timing on an instantaneous percycle basis to allow for instantaneous changes in cyclic parameters. This may be more clearly explained with reference to FIG. 3.

EMBODIMENT OF FIGURE 3 In FIG. 3, a modification of the control means of FIG. 2 is provided for automatic change in the time relationship between the operation of the combustion-causing means and the moment of power piston reversal. In this case, control means 12A is basically similar to control means 12 of FIG. 2, with the following changes. Control cylinder 66 has an additional automatically variable outlet valve in a vertically extending conduit 136 communicating with control chamber 64.

The vertically upward extending leg 136 includes a horizontally arranged, rightward extending boss 137 formed thereon. Pivotally attached to boss 137 is a lever 138 having lever arms 139 and 141. Lever arms 139 and 141 are arranged at an obtuse angle with respect to one another and have their inner ends connected together and pivotally connected to boss 137 at a fulcrum 142. A horizontally arranged link 143 is connected to the outer end of lever arm 139 which is shown in a vertical position. Link 143 interconnects arm I39 and a horizontally arranged sliding valve member 144 which is positioned in conduit 136 to further control the rate of escape of fluid from the control chamber 64. More particularly, sliding valve member 144 includes a passage 146 formed therein, and valve member 144 is arranged to be horizontally movable so that passage 146 provides a variable valve opening for conduit 136. As sliding valve 144 is horizontally moved, more or less of passage 146 is effective within conduit 136 to control the escape of gas from control chamber 64 to the atmosphere. As will be appreciated by those skilled in the art, passage 146 may be tapered, triangular, circular, elliptical, or many other shapes in cross section to achieve the desired control effect.

Arm 141, which is arranged at an angle below the horizontal, has a shaft 148 connected to its outer end. Shaft 148 interconnects lever arm 141 with a damper piston 150 arranged to vertically reciprocate within a damper cylinder 151 connected to the end 88 of control cylinder 66. Thus, a damper chamber area 154 is formed above piston 150 and within damper cylinder 151. Tubular cylinder end 88 provides fluid communication between end 152 of cylinder 151 and the controlled orifice 90. A further bleed passage 153 provides fluid communication to the atmosphere from chamber 154 for damping control. The rightward extending end 88 of control cylinder 66 provides fluid communication between the control chamber 64 and cylinder end 152. Thus, gas compressed within control chamber 64 can act upon the lower surfaceof piston 150 against the action of a spring 155 positioned between the upper face of piston 150 and a hollow center, adjustment screw 156 positioned in the top of damper cylinder 151 to allow the passage of shaft 148 and seal chamber 154. Thus the effective orifice in conduit 136 can be controlled automatically.

The basic operation of the embodiment of FIG. 3 is substantially identical to that explained with respect to FIG. 2. Piston 54 creates a pressure within sensing chamber 57 and control chamber 64 which causes the leftward movement of piston 70 and the closing of ignition points 112. In FIG. 3, however, this same pressure within chamber 64 is used to control the variable orifice 146 through which fluid within chamber 64 may pass to the atmosphere and hence automatically correctly position the initiation of combustion in time on an instantaneous per cycle basis.

In particular, the pressure within control chamber 64 also supplies a force to auxiliary piston 150 which is again proportional to this pressure. The force supplied to piston 150 moves shaft 148 upward against the bias of return spring 155 and moves sliding valve 144 leftward to expose more of passage 146 to the interior of conduit 136. With more of passage 146 exposed, more compressed gas within chamber 64 may escape to the atmosphere, and the timing of initiation of combustion is changed.

Thus, under normal operating conditions, the force exerted upon auxiliary piston 150 is such as to expose a given amount of the passage 146 to the conduit means 136. Upon a misfire, the energy provided from combustion chamber 135 for a stroke to the left is only the energy stored in the compressed gas or fuel gas mixture within combustion chamber 135 and in the clearance volume of compressor chamber 34. This decrease in energy moving the pistons to the left causes a significant decrease in the amount of energy which may be stored in positive bounce chamber 42, and hence velocity of power piston on its next power stroke to the right is reduced. The reduction of velocity of power piston 20 causes a corresponding reduction in velocity of sensing piston 54 and a corresponding decrease in the pressure created within control chamber 64. A decrease in the pressure created in chamber 64 exerts a smaller force upon auxiliary piston 150 which decreases the distance through which shaft 148 moves lever 138 and hence decreases the exposure of passage 146 to the interior of conduit means 136. This decrease in exposure decreases the volume of gas escaping from chamber 64 and has a tendency to increase the resulting control pressure corresponding to a particular instantaneous piston velocity and thus modify or maintain the desired timing of combustion with reference to the inner reversal point of power piston 20. Hence, when a misfire occurs which would cause a slower and shorter return stroke, the apparatus of FIG. 3 automatically adjusts the control pressure in chamber 64 to compensate for the misfire. Then, with the decreased exposure of passage 146 and the resulting decreased bleed rate from chamber 64, the pressure upon auxiliary piston 70 is maintained at adequate levels, even though the volume rate of pressure input from sensor 54 is decreased. This helps insure the making and breaking of the contacts at a suitable time interval related to the inner reversal point of the power piston, even after the occurrence ofa misfire.

Damper 152 in effect uses a pressure indication of the peak or maximum value of the velocity of power piston 20 as a further reference factor, so that the initiation of ignition may be automatically controlled for slight cycle to cycle variations as well as for substantial variations, such as a misfire.

Controlled orifice 90 provides a further control of the rate of pressure escape from chamber 64, just as in the device of FIG. 2. Bleed opening 153 controls the speed at which damper piston 150 returns downwardly, since gas must enter chamber 154 above piston 150 before piston 150 may move back downwardly under the urging of spring 155. Bleed opening 153 may be provided with an adjustable orifice, and damper chamber 154 may have a one-way escape check valve to facilitate upward movement of damper piston 150, if desired. Although not shown in FIG. 3, such items are shown at 186 and 183 in FIG. 7.

Controlled orifices at and 153 may also be used to control the rate of recovery of piston to a neutral position during the power stroke of power piston 20 when sensing piston 54 is moving to the left. Thus, the previous indication of the maximum velocity of power piston 20 stored in damper 151 in terms of the piston of damper piston 150 is removed, and an indication of the instantaneous maximum velocity of the next power stroke of power piston 20 may be applied to or stored in damper 151.

EMBODIMENT OF FIGURE 5 The modified control means 123 shown in FIGS. 5 through 7 is designed to provide a modification of the pressure in control chamber 64, which is related to the acceleration of the free piston 20. In this case the control cylinder 66 again provides a pressure chamber 64 in which the control pressure acts on piston 70 to make and break the ignition breaker points 112. The escape of pressure from control chamber 64 is controlled in this embodiment by a slide valve which has an orifice 161 of tapered shape as shown in FIG. 6. Vertical upward movement of member 160 decreases the effect of bleed orifice 161 by moving a portion or all of such opening 161 out of the cross section of end 88 of the control cylinder 66. The sooner valve opening 161 moves up, the earlier the control pressure in chamber 64 will increase to a particular level, and vice versa. Thus, the rate of relief of pressure through opening 161 to the atmosphere, which depends on the vertical position of member 160, can'vary the relative timing of combustion.

Valve member 160 is connected at 162, by a mechanism shown in detail in FIG. 7, to a vertically movable cam follower rod 163 supported by guide 164 which provides an opening in the engine housing. The lower end of rod 163 carries a cam follower 166 adapted to engage and ride on the sloping cam surface 167 of a cam 168 fixed to the power piston shaft 24 (or to another engine part which moves with instantaneous accelerations proportional to those of the power piston). The slope of cam 167 is exaggerated for convenience in description and understanding. Spring 169 urges cam follower 166 into engagement with cam surface 167 at all times.

The interior of shaft 163 is recessed at 171 to receive a connection from the valve member 160. As shown in FIG. 7, this valve member has a head portion 172 of substantial mass and a cylindrical downwardly projecting skirt 173 which surrounds the upper end of shaft 163. A connecting shaft 174 extends from head portion 172 into the hollow center 171 of cam follower shaft 163. A nut or other retainer 176 holds the parts in the assembled relationship of FIG. 7 so that they will not be completely separated in a vertical direction, but may have relative movement with respect to each other in both directions along their common vertical axis. An internal spring 177 normally urges the valve member 160 upwardly with respect to hollow rod 163, but the spring constant and length of this spring are such that retaining nut 176 is normally spaced below the upper end of the hollow chamber 171. Thus, there is still room for member 160 to be projected upwardly beyond the relative position of FIG. 7.

A sealing ring 178 on the upper end of hollow rod 163 makes this rod end serve as a piston within the cylindrical portion 173, thus providing a pressure chamber 181 within member 173 between rod 163 and the valve member head 172. A passage 182 in head 172 connects chamber 181 with a one-way spring loaded exhaust check valve 183 and permits the release of pressure within chamber 181, if there is sudden increase in such pressure. Passage 182 also communicates with a bleed opening 184, the area of which may be manually preset by a needle valve member 186. In effect, the construction shown in detail in FIG. 7 provides an acceleration-responsive connection between the valve member 160 and the cam follower shaft 163.

In operation, if the piston assembly is moving slowly to the right on a compression stroke, the resulting upward movement of cam follower shaft 163 would be slow enough, so that spring 177 could transmit this movement directly to the head portion 172 and valve member 160. Then these parts, despite their mass and inertia, would move upwardly as a unit to provide one desired relative valve position for conduit 161. If, however, the movement of the piston assembly to the right is occuring at a higher acceleration, the cam follower shaft 163 will be accelerated upwardly faster than spring 177 can overcome the inertia of mass 172 and other parts of valve member 160. Air will thus be driven suddenly out of chamber 181 through check valve 183, and the effective length of the acceleration-responsive connection 162 will be shortened temporarily. Thus, a different desired relative area of opening 161 will be available for release of pressure from control chamber 64 or for restoration of pressure therein. The effective length of variable connection 162 will then slowly increase back to normal, as air is permitted to bleed back into chamber 181 through adjustable orifice 184.

In operation, by proper select-ion of the shape and position of opening 161 and orifice 184, when the velocities are higher and the acceleration-responsive linkage is shorter, the effective control air passage for bleeding the pressure from control chamber 64 can be automatically varied, so that timing of the breaking action of the ignition contacts will come sooner and the spark will becorrespondingly advanced for higher speeds of operation. When the acceleration of the piston to the right is slower, the effective length of the acceleration-responsive connection 162 will be longer and the bleed action of valve member 160 can be automatically changed the other way, so the spark will occur later, with reference to the moment of piston reversal.

EMBODIMENT OF FIGURE 8 FIG. 8 shows another preferred embodiment of the invention which includes special timing means for adjusting the time relationship between the sensing signal and the combustion causing signal and thus varying the time relationship between the moment of combustion and the moment of piston reversal at the end of a compression stroke. The device is designed to provide a properly timed initiation of combustion during a relatively slow compression stroke as well as a different, but properly timed, initiation of combustion during a relatively fast compression stroke.

In this embodiment, sensing piston 54 on its shaft 52 is again responsive to a movement-related characteristic of the power piston, i.e., its velocity and acceleration. .The pressure signal from this sensor, which is generated in chamber 57 of the sensing cylinder in the manner previously described, is fed to a vertical cylinder 62 which extends upwardly and has a closed upper end 188. At the top of this vertical cylinder 62, which provides in its interior the desired control pressure chamber 64, a two-part housing is supported. Between the lower part 189 and upper part 191 of this housing a flexible diaphragm 192 is secured in known manner, so that the central portion of the diaphragm is free to flex vertically along the axis of the cylinder 62.

A vertical shaft 193, extending vertically along the axis of cylinder 62, has its lower end secured to a piston 194 in the upper end of cylinder 62. Between piston 194 and the closed end 188 of the cylinder, a spring 196 is supported in a manner to resist upward movement of the control piston 194 and thus provide a measuring or reference force. Normally spring 196 will hold piston 194 downwardly far enough within cylinder 62, so that the piston provides a complete closure for the control chamber 64. One or more vents 197 are provided in the sidewall of control cylinder 62 at a vertical location somewhat above the normal rest position of piston 194, so that these vents are normally closed at the start of a cycle. Generation of a predetermined pressure signal at 57, and its transmission to the control chamber 64, will result in upward movement of the piston 194 and shaft 193. At a predetermined position in this upward movement, the vents 197 will be open to a lesser or,

greater degree to provide a venting or bleeding action for the pressure chamber 64.

The upper end 198 of shaft 193 is secured by a telescoping connection within an output member 199. Within member 199 a spring 201 tends to urge the upper end 202 of this output member upwardly, relative to shaft 193, toward or into en gagement with the operating arm of movable contact 116 of breaker points 116 and 120. Spring 201 and the telescoping connection between the upper end 198 of shaft 193 and the output member 199 provide a slidable connection which permits an override under certain operating conditions.

Thus, in normal operation, the parts will be in a position where contacts 116 and 120 of the breaker points are separated. During a compression stroke, while piston 54 moves to the right in FIG. 8, the generation of a predetermined pressure level in chamber 64 urges piston 194 upwardly until the output end 202 of member 199 operates the movable contact arm and closes the points to make" the ignition circuit through the usual primary coil. If the pressure in chamber 64 is great enough to urge shaft 193 still higher, the override provided by spring 201 permits this vertical movement of shaft 193, while the contacts remain in the same closed position.

According to this preferred embodiment the vertically movable shaft 193 is secured at 203 to the central portion of diaphragm 192. Suitable stops 204 can be provided to limit the maximum vertical flexing of this diaphragm in either direction within safe limits for the diaphragm itself or the other parts. The construction provides controllably vented dashpot or air chamber 206 above diaphragm 192 within housing 191. Thus, upward movement of shaft 193 and the central portion of the diaphragm tends to compress the air within chamber 206. A relatively easily operable one-way check valve 207 permits the free venting of pressure outwardly from chamber 206 during upward movement of diaphragm 192, but prevents the inward flow of air through valve 207, when the diaphragm tries to move downwardly.

A separate controllable air inlet 208 is provided for the dashpot or damper chamber 206. This inlet 208 is controlled by a variable orifice shown schematically at 209, which may be adjusted to provide a desired rate of restoration of normal ambient pressure within chamber 206. Thus, the operator may modify or adjust the timing at which diaphragm 192 and shaft 193 can move downwardly to permit breaking of contacts 116 and 120 to cause a spark 'within the engine combustion chamber. Spring 196 may be adjustable as at (FIG. 1).

A further adjustable bleed passage 211 is provided to adjust the rate of pressure relief from the pressure control chamber 64. Thus, passage 211 communicates with chamber 64 at a point 212 which will always be exposed to the pressure in chamber 64 regardless of the vertical upward or downward movement of piston 194. An adjustable orifice 213 controls the volume or rate of relief of pressure through conduit 211 from chamber 64 and thus helps determine the desired timing.

As shown schematically at 214 and 216 in FIG. 8, the adjustable orifice 213 may be. controlled in response to the output pressure of compressor 34 or in response to some other operating characteristic, which reaches a predetermined level when the engine achieves normal operation. In this embodiment of the invention the orifice 213 is intended to remain essentially closed, whenever the compressor pressure or other selected operating characteristic is below the level achieved during normal operation of the engine. Thus, on a slow compression stroke, prior to normal operation of the engine or following a previous misftre, pressure control chamber 64 will have essentially no outlet. The pressure will then build up in chamber 64 more rapidly as the power piston and its associated sensing piston 54 move to the right during such a compression stroke. Thus, the generation of a sufficient presnun-U sure control signal in chamber 64 to cause the making and breaking of the ignition contacts is assured, even during a relatively slow and/or short power piston stroke to the right Once the engine is operating more normally and thus at higher speeds, orifice 211 can be opened by connecting means 216 responsive to the sensing at 214 of the selected operating characteristic. The rate of pressure relief from chamber 64 is thereby increased to facilitate optimum ignition timing during normal high-speed strokes. To restore the desired pressure from the start ofa new cycle, a one-way valve 218 may be provided in chamber 57 of the embodiment of FIG. 8. Such a valve may also be helpful in restoring such pressure in the other embodiment of FIGS. 2, 3 and 5.

The same sort of control, based on sensing of any desired characteristic of the engine or its load (such a load sometimes being referred to generically as an energy absorbing device) may be used to vary the adjustable orifice 209 in the device of FIG. 8, or any other adjustable orifice, such as the orifices 90 in the embodiments ofFIGS. 3 and 5.

CONCLUSION Thus a method and apparatus have been disclosed for controlling the initiation of combustion within a free piston engine around the time of reversal of the power piston within the power cylinder at the end of a compression stroke and the start of a power stroke. This timing of the initiation of combustion may be controlled without regard to variations in the actual physical location of the power piston in the power cylinder at its moment of reversal after different compression strokes.

Thus the present invention allows much more freedom in designing free piston engines than heretofore possible. A misfire or other source of trouble which would have prevented the power piston in a prior art free piston engine from achieving its desired inner reversal or dead point need not stop the engines of the present invention.

Moreover, the apparatus of each of FIGS. 2, 3, 5 and 8 can effectively prevent premature initiation of combustion on the compression stroke of power piston at a point in time before the maximum piston velocity is reached. Ignition is prevented during this time, since there is a continual buildup of the sensing signal input to the control means due to the increasing velocity of piston 54 'and the controlled low volume rate of pressure relief from control chamber 64. Combustion is then preferably initiated only after the maximum value of power piston velocity has been reached on the compression stroke and the velocity of power piston 20 and sensing piston 54 is decreasing.

Now that the basic teachings of the present invention have been explained, many extensions and variations will be obvious to one skilled in the art. For example, apparatus other than that shown in FIGS. 2 through 8 may perform the functions of the blocks indicated in FIG. 1. For example, electrical signal generation means may be employed, both for sensing and for control, or either of these means. No limitation to the precise apparatus of type of signal is intended. Also, in the acceleration-responsive modifications of the invention, many different combinations of movable mass and spring arrangements or of other acceleration-responsive controls will be apparent to those skilled in the art for practicing the sensing, measuring and/or timing features of this invention.

Further, while it is of particular advantage to utilize a sensing or control signal from a parameter proportional to the peak of the velocity of the power piston, many other techniques are possible including the creation of a reference signal from the initial slope of the characteristic or parameter sensed, rather than from the maximum value since, in the case of many parameters, the initial slope contains information closely related to that of the maximum value.

Finally, it will be apparent that the invention includes the use of either a single power piston movement-related characteristic, or the use of more than one such characteristic, or the modification of sensing signals analogous to one or more such characteristic by sensing signals generated in response to some other engine or load device characteristic, to provide the desired time relationship between the moment of ignition and the moment of piston reversal at the end of a compression stroke.

Also, while the foregoing description has emphasized the sensing, measurement and timing of signals generated during the compression stroke of a free piston engine, it will be apparent that the preferred embodiments, particularly those involving pressure generation and response, can be designed to take into consideration the effects on the system of the return stroke. The effects during such a power stroke, for example, the suction produced within a pressure sensing cylinder by the return movement of a pressure sensing piston and the manner in which various orifices permit entrance of air back into the system for a new cycle, must be considered. In certain cases the position of the power piston at some point other than the particular point of reversal which is to be anticipated for timing the start ofcombustion may be used as a factor in conjunction with other characteristics to control or adjust the timing.

The foregoing specification has accordingly set forth the nature and principles of the present invention together with illustrative variations in the preferred embodiments by which the invention may be practiced.

Now, therefore, what is claimed is:

1. In a free piston engine having a power cylinder, a movable piston assembly including a power piston is freely reciprocable in said cylinder and in which a power stroke in one direction immediately follows a compression stroke in the opposite direction, and combustion-causing means for initiating combustion in the cylinder to move the power piston in the one direction for each successive power stroke, the improvement comprising sensing means responsive to a movement-related power piston characteristic which has a predeterminable relationship to the moment when the power piston reaches a reversal point at the end of each compression stroke, and which is substantially independent of variations in the actual physical position of the piston along said path at the moment of piston reversal for different power strokes, the sensing means providing a sensing signal analogous to the instantaneous values of the movement-related power piston characteristic, and control means connected to receive the sensing signal from the sensing means, the control means also having means responsive to a predetermined sensing signal for operating the combustion-causing means at a point in time having a desired combustion timing relationship with respect to the moment of power piston reversal 'at the end of each compression stroke.

2. Free piston engine apparatus according to claim 1, in which said control means includes adjustable timing means for adjusting the relative time relationship between the actuation of the combustion-causing apparatus and the moment of piston reversal at the end of the compression stroke.

3. Free piston engine apparatus according to claim 1 in which the sensing means includes means providing a sensing signal proportional to the instantaneous velocity of the power piston, and said control means includes means responsive to a predetermined change in said signal for actuating the combustion initiating apparatus.

4. Free piston engine apparatus according to claim 1 in which said control means includes measuring means connected for receiving the sensing signal and determining its value.

5. Free piston engine apparatus according to claim 4 in which the sensing means includes a pressure sensing cylinder and a pressure sensing piston, one of which is connected to move as a unit with the power piston; the control means includes a control pressure chamber and means connecting the pressure sensing cylinder to the control pressure chamber to provide a control pressure therein; the measuring means includes a movable auxiliary piston exposed to the pressure in the control pressure chamber for movement of the auxiliary piston in one direction in response to increasing control pressure, and adjustable resilient means connected to urge the auxiliary piston in the opposite direction against the control pressure; and means operatively connected to the auxiliary piston for operating the combustion-causing means in response to predetermined movement of the auxiliary piston in the one direction.

6. Free piston engine apparatus according to claim 5 in which the control means also includes adjustable timing means for modifying the control pressure in the control pressure chamber, the timing means including adjustable orifice means connecting the control pressure chamber to an ambient pressure different from the control pressure, and means for adjusting the orifice means.

7. Free piston engine apparatus according to claim 6 in which the means for adjusting-the orifice means is manually adjustable.

8. Free piston engine apparatus according to claim 7 in which the means for adjusting the orifice means is automatically responsive to an operating characteristic of the engine.

9. Free piston engine apparatus according to claim 8 in which the means for adjusting the orifice means is responsive to predetermined acceleration of the power piston.

10. Free piston engine apparatus according to claim 2 in which the adjustable timing means and the sensing means are both responsive to the same movement-related power piston characteristic.

11. Free piston engine apparatus according to claim 2 in which the adjustable timing means and the sensing means are respectively responsive to different movement-related power piston characteristics.

12. Free piston engine apparatus according to claim 11 having a member operatively connected for movement in response to predetermined accelerations of thepower piston, and means operatively connecting the acceleration-responsive member with the adjustable timing means and thereby adjusting the timing means in response to the predetermined accelerations.

13. An improved method of controlling combustion in a free piston engine having a power cylinder and a power piston freely reciprocable in the power cylinder along a path between desired normal inner and outer piston reversal points which may vary from from stroke to stroke, and in which a power stroke in one direction immediately follows a compression stroke in the opposite direction, comprising the steps of a. sensing a movement-related power piston characteristic which has a predeterminable relationship to the moment when the power piston reaches a reversal point at the end of each compression stroke, and which is substantially independent of variations in the actual physical position of the piston along said path at the moment of piston reversal for different power strokes,

b. providing a sensing signal related to the instantaneous value of the sensed characteristic,

c. measuring the sensing signal, and

d. initiating combustion for a power stroke of the power piston, when the measurement of the sensing signal indicates that a desired predetermined time relationship of the sensed characteristic to the moment of power piston reversal has been reached.

14. An improved method of controlling combustion in a free piston engine having a power cylinder and a power piston reciprocally moving in the power cylinder between an inner dead point and an outer dead point so as to compress gases Ital point, said method comprising the steps of:

a. sensing a movement-related parameter of the power piston which has a predeterminable time relationship to the moment of piston reversal at the inner dead point and providing a sensing signal analogous to the instantaneous value of the movement related parameter sensed,

b. measuring the sensing signal analogous to the instantaneous-value of the movement-related parameter sensed, and

c. initiating combustion when the measurement of the sensing signal indicates that the predetermined time relationship to the moment of reversal has been reached.

15'. The method of claim 14 wherein step (b) further comprises:

l. comparing the sensing signal to a reference signal,

2. storing the maximum instantaneous value of the sensing signal during each cycle of the engine, and

3. adjusting one of the sensing and reference signals in relation to the stored maximum value of the sensing signal.

16. The method of claim 14 wherein the movement-related parameter reaches a fixed value at the two times per cycle the power piston reverses direction in the power cylinder and the movement-related parameter has a smoothly varying value between these two times, the value starting at the fixed value when the power piston is at its outer reversal point, the value increasing to a peak during the time the power piston travels the first part of its stroke from its outer reversal point to its inner reversal point on its compression stroke, and the value declining from the peak to the fixed value as the power piston completes the remaining part of its stroke and again stops at its inner reversal point, wherein step (a) further comprises the steps of:

1. storing an indication of the peak of the movement-related parameter during a single compression stroke,

2. adjusting the signal analogous movement-related parameter sensed in relation to the indication of the peak of the movement-related parameter stored, and

3. removing the indication of the peak of the movementrelated parameter stored after combustion is initiated whereby an indication of the next peak of the movement-related parameter may be independently stored.

17. The method of claim .14 wherein the movement related parameter reaches a fixed value at the two times cycle the power piston reverses direction in the power cylinder and the movement related parameter has a smoothly varying value between these two times, the value starting at the fixed value when the power piston is at its outer reversal point, the value increasing to a peak during the time the power piston travels the first part of its stroke from its outer reversal point to its inner reversal point on its compression stroke, and the value declining from the peak to the fixed valueas the power piston completes the remaining part of its stroke and again stops at its inner reversal point, and wherein step (c) includes the step of initiating combustion when the measured value of the sensing signal indicates that the value of the sensed parameter has declined a predetermined percentage of the difference between its peak value and its fixed value. 

1. In a free piston engine having a power cylinder, a movable piston assembly including a power piston is freely reciprocable in said cylinder and in which a power stroke in one direction immediately follows a compression stroke in the opposite direction, and combustion-causing means for initiating combustion in the cylinder to move the power piston in the one direction for each successive power stroke, the improvement comprising sensing means responsive to a movement-related power piston characteristic which has a predeterminable relationship to the moment when the power piston reaches a reversAl point at the end of each compression stroke, and which is substantially independent of variations in the actual physical position of the piston along said path at the moment of piston reversal for different power strokes, the sensing means providing a sensing signal analogous to the instantaneous values of the movementrelated power piston characteristic, and control means connected to receive the sensing signal from the sensing means, the control means also having means responsive to a predetermined sensing signal for operating the combustion-causing means at a point in time having a desired combustion timing relationship with respect to the moment of power piston reversal at the end of each compression stroke.
 2. Free piston engine apparatus according to claim 1, in which said control means includes adjustable timing means for adjusting the relative time relationship between the actuation of the combustion-causing apparatus and the moment of piston reversal at the end of the compression stroke.
 2. storing the maximum instantaneous value of the sensing signal during each cycle of the engine, and
 2. adjusting the signal analogous movement-related parameter sensed in relation to the indication of the peak of the movement-related parameter stored, and
 3. removing the indication of the peak of the movement-related parameter stored after combustion is initiated whereby an indication of the next peAk of the movement-related parameter may be independently stored.
 3. adjusting one of the sensing and reference signals in relation to the stored maximum value of the sensing signal.
 3. Free piston engine apparatus according to claim 1 in which the sensing means includes means providing a sensing signal proportional to the instantaneous velocity of the power piston, and said control means includes means responsive to a predetermined change in said signal for actuating the combustion initiating apparatus.
 4. Free piston engine apparatus according to claim 1 in which said control means includes measuring means connected for receiving the sensing signal and determining its value.
 5. Free piston engine apparatus according to claim 4 in which the sensing means includes a pressure sensing cylinder and a pressure sensing piston, one of which is connected to move as a unit with the power piston; the control means includes a control pressure chamber and means connecting the pressure sensing cylinder to the control pressure chamber to provide a control pressure therein; the measuring means includes a movable auxiliary piston exposed to the pressure in the control pressure chamber for movement of the auxiliary piston in one direction in response to increasing control pressure, and adjustable resilient means connected to urge the auxiliary piston in the opposite direction against the control pressure; and means operatively connected to the auxiliary piston for operating the combustion-causing means in response to predetermined movement of the auxiliary piston in the one direction.
 6. Free piston engine apparatus according to claim 5 in which the control means also includes adjustable timing means for modifying the control pressure in the control pressure chamber, the timing means including adjustable orifice means connecting the control pressure chamber to an ambient pressure different from the control pressure, and means for adjusting the orifice means.
 7. Free piston engine apparatus according to claim 6 in which the means for adjusting the orifice means is manually adjustable.
 8. Free piston engine apparatus according to claim 7 in which the means for adjusting the orifice means is automatically responsive to an operating characteristic of the engine.
 9. Free piston engine apparatus according to claim 8 in which the means for adjusting the orifice means is responsive to predetermined acceleration of the power piston.
 10. Free piston engine apparatus according to claim 2 in which the adjustable timing means and the sensing means are both responsive to the same movement-related power piston characteristic.
 11. Free piston engine apparatus according to claim 2 in which the adjustable timing means and the sensing means are respectively responsive to different movement-related power piston characteristics.
 12. Free piston engine apparatus according to claim 11 having a member operatively connected for movement in response to predetermined accelerations of the power piston, and means operatively connecting the acceleration-responsive member with the adjustable timing means and thereby adjusting the timing means in response to the predetermined acceLerations.
 13. An improved method of controlling combustion in a free piston engine having a power cylinder and a power piston freely reciprocable in the power cylinder along a path between desired normal inner and outer piston reversal points which may vary from from stroke to stroke, and in which a power stroke in one direction immediately follows a compression stroke in the opposite direction, comprising the steps of a. sensing a movement-related power piston characteristic which has a predeterminable relationship to the moment when the power piston reaches a reversal point at the end of each compression stroke, and which is substantially independent of variations in the actual physical position of the piston along said path at the moment of piston reversal for different power strokes, b. providing a sensing signal related to the instantaneous value of the sensed characteristic, c. measuring the sensing signal, and d. initiating combustion for a power stroke of the power piston, when the measurement of the sensing signal indicates that a desired predetermined time relationship of the sensed characteristic to the moment of power piston reversal has been reached.
 14. An improved method of controlling combustion in a free piston engine having a power cylinder and a power piston reciprocally moving in the power cylinder between an inner dead point and an outer dead point so as to compress gases within the power cylinder as the power piston moves from its outer dead point to its inner dead point, said method comprising the steps of causing combustion to occur at a predetermined time relationship to the time the power piston reverses direction at its inner dead point without regard to variations from one stroke to another in the actual position of the power piston in the cylinder at the moment it reaches the inner dead point, said method comprising the steps of: a. sensing a movement-related parameter of the power piston which has a predeterminable time relationship to the moment of piston reversal at the inner dead point and providing a sensing signal analogous to the instantaneous value of the movement related parameter sensed, b. measuring the sensing signal analogous to the instantaneous value of the movement-related parameter sensed, and c. initiating combustion when the measurement of the sensing signal indicates that the predetermined time relationship to the moment of reversal has been reached.
 15. The method of claim 14 wherein step (b) further comprises:
 16. The method of claim 14 wherein the movement-related parameter reaches a fixed value at the two times per cycle the power piston reverses direction in the power cylinder and the movement-related parameter has a smoothly varying value between these two times, the value starting at the fixed value when the power piston is at its outer reversal point, the value increasing to a peak during the time the power piston travels the first part of its stroke from its outer reversal point to its inner reversal point on its compression stroke, and the value declining from the peak to the fixed value as the power piston completes the remaining part of its stroke and again stops at its inner reversal point, wherein step (a) further comprises the steps of:
 17. The method of claim 14 wherein the movement related parameter reaches a fixed value at the two times cycle the power piston reverses direction in the power cylinder and the movement related parameter has a smoothly varying value between these two times, the value starting at the fixed value when the power piston is at its outer reversal point, the value increasing to a peak during the time the power piston travels the first part of its stroke from its outer reversal point to its inner reversal point on its compression stroke, and the value declining from the peak to the fixed value as the power piston completes the remaining part of its stroke and again stops at its inner reversal point, and wherein step (c) includes the step of initiating combustion when the measured value of the sensing signal indicates that the value of the sensed parameter has declined a predetermined percentage of the difference between its peak value and its fixed value. 